host-bacteria interactions

Question 1

what are virulence factors

Answer 1

Molecules that allow bacteria to adhere, invade, evade host defence, cause tissue damage, replicate or persist in the host

Question 2

what is a virulence gene

Answer 2

Gene encoding a virulence factor

Question 3

how have virulence genes evolved

Answer 3

horizontal transfer of virulence genes => rapid evolution
- Plasmids
- Transposons
- Phage transduction

Question 4

outline the steps in the bacterial infection process

Answer 4

1. adhesion
2. invasion (intra/extra cellular survial)
3. subversion of host defence
4. replication
5. long term survival in host OR spread to further hosts (survival in environment)

Question 5

describe adhesion

Answer 5

bacteria attach to cells, secretory products, structural components and other bacteria
via: fimbriae/pili, adhesive macromolecules imbedded in membrane, capsules, flagellum, proteinaceous fibrils

Question 6

what strategies do bacteria use to survive the host defense

Answer 6

• resistance to host defence
• Active subversion of host defence (killing of phagocytic or changing host cell)

Question 7

how do bacteria resist the host defence

Answer 7

• complement resistance (long polysaccharide chains to inhibit binding and capsule)
• avoiding phagocytosis (capsules, M proteins, production of Fc-binding proteinfs to prevent interaction with Fc receptors on phagocytes)
• protection against recognition by antibodies

Question 8

how do bacteria survive by active subversion of host defence

Answer 8

1. toxins
2. superantigens
3. bacterial effector proteins injected into host cells

Question 9

compare intacellular vs extracellular survival of bacteria

Answer 9

intracellular:

• not exposed to immune cells, antibiotics, defensins or complement
• limited nutrients

extracellular:

• exposed to immune cells, antibodies, defensins and complement
• nutrient rich (lots of glc, glutamine), iron limited

Question 10

describe how streptococcus equi survives extracellularly

Answer 10

• prevention of phagocytosis (has hyaluronase capsule, antiphagocytic enzymes, M-proteins, binding of fibrinogen to mask binding sites)
• rapid killing of neutrophils (toxins production)

Question 11

how do bacteria get inside cells

Answer 11

• phagocytic cells (pro: will take up actively bacteria, con: deigned to kill bacteria - need to interrupt process of digestion to survive)
• forced phagocytosis (manipulate cells to phagocytose bacteria

Question 12

how do bacteria move inside cells

Answer 12

manipulation of host cytoskeleton (actin and microtubules)

Question 13

how do bacteria obtain nutrients inside the cells

Answer 13

manipulation of host metabolism (poor access to nutrients inside cells and even worse inside vacuole)